A disturbance (change in position or state of individual particles) in the fabric of space-time causes a sphere of influence. Stated in a simplistic manner, the action of one particle influences the actions of the others near it. This sphere of influence is referred to as a "field", and this field is designated as either electric or magnetic (after the way it influences other particles). The direction of travel of the particle is called the direction of propagation. The propagation of the particle, the sphere of influence, and the way it influences other particles is called an electromagnetic wave, and is shown in FIG. 1.
As shown in FIG. 1, the electric and magnetic fields are orthogonal (at right angles) to each other and the direction of propagation. These fields can be mathematically expressed as a vector quantity (indicating the direction of influence along with strength, i.e., magnitude, of influence) at a specific point or in a given region in space. Thus, FIG. 1A is the electromagnetic wave in FIG. 1, but with the view of looking down the axis of propagation, that is, down the x axis of FIG. 1. FIG. 1A shows some possible various electric field vectors that could exist, although it should be understood that any and all possible vectors can exist around the circle, each having different magnitudes.
Vectors can be resolved into constituent components along two axes. This is done for convenience sake and for generating a frame of reference that we, as humans, can understand. By referring to FIG. 1B, it is shown that the electric field vector E, can be resolved into two constituent components, E(y) and E(x). These quantities, then, describe the orientation and the magnitude of the electric field vector along two axes, the x and y, although other axes or systems could be chosen. The same applies to magnetic fields, except that the X and Z axes would be involved.
The way the electric and magnetic fields vary with time in intensity and direction of propagation have been determined by several notable mathematicians and physicists, culminating in a group of basic equations by James Maxwell. These equations, simply applied, state that a field vector can be of one of several different states, that is: 1) the field vector varies randomly over a period of time, or 2) the field vector can change directions in a circular manner, or 3) the field vector can change directions in a elliptical manner, or 4) the field vector can remain constant in magnitude and direction, hence, the field vector lies in one plane, and is referred to as planar.
This orientation of a field vector and the way it changes with time is called the state of polarization.
Electromagnetic waves can be resolved into separate electromagnetic waves with predetermined orientations of a field vector. The electromagnetic waves with a predetermined orientation of a field vector can then be directed through materials, such as a liquid crystal device, that is capable of changing (or altering) their orientation of the field vector upon application of an outside stimulus, as is demonstrated in FIG. 7. These devices are noted as programmable electromagnetic wave field orientation rotating devices (PEMFVORD).
An electromagnetic wave can be characterized by its frequency or wavelength. The electromagnetic spectrum (range) extends from zero, the short wavelength limit, to infinity, the long wavelength limit. Different wavelength areas have been given names over the years, such as cosmic rays, alpha rays, beta rays, gamma rays, X-rays, ultraviolet, visible light, infrared, microwaves, TV and FM radio, short wave, AM, maritime communications, etc. All of these are just short hand expressions of stating a certain range of frequencies for electromagnetic waves.
Different areas of the spectrum interact with electromagnetic influences upon them in various proportions, with the low end being more influenced by magnetic fields, and the high end being influenced by electric fields. Thus to contain a nuclear reaction, a magnetic field is used, while controlling light an electric field is used.
FIG. 2 illustrates a schematic cross section of an LCD cell. The LCD cell 100 includes a liquid crystal material 101 that is contained between two transparent plates 103, 104. Spacers 105, 106 are used to separate the transparent plates 103, 104. Sealing elements 107, 108 seal the liquid crystal material 101 between the transparent plates 103, 104. Conductive coatings 109, 110 on the transparent plates 103, 104 conduct the appropriate electrical signals to the liquid crystal material 101.
A type of liquid crystal material 101 used in most LCD cells for optical display systems is referred to as "twisted nematic." In general, with a twisted nematic LCD cell, the molecules of an LCD cell are rotated in the absence of a field through a 90.degree. angle between the upper 103 and lower 104 transparent plates. When a field is applied, the molecules are untwisted and line up in the direction of the applied field. The change in alignment of the molecules causes a change in the birefringence of the cell. In the homogeneous ordering, the birefringence of the cell changes from large to small whereas the opposite occurs in the homeotropic case. The change in birefringence causes a change in the orientation of the electric field vector for the light being passing through the LCD. The amount of the rotation in the molecules for an individual LCD cell 100 will determine how much change in polarization (orientation of the electric field vector) of the light occurs for that pixel. The light beam is then passed through another component of the system (i.e., polarizer analyzer) and is resolved into different beams of light by the orientation of their electric field vectors, with the light that has a selected predetermined component of the electric field vector passing through to finally strike the screen used for the display.
A twisted nematic LCD cell requires the light incident at the LCD cell 100 to be polarized. The polarized light for a typical projector is generally derived from a randomly polarized light source that is collimated and then filtered by a plastic polarizer to provide a linear polarized beam. Linear polarized beams are conventionally referred to as being S-polarized and P-polarized with the P-polarized beam defined as polarized in a direction parallel to the plane of incidence and the S-polarized beam defined as polarized perpendicular to the plane of incidence.
The development of PEMFVORD technology has resulted in the development of LCD projectors which utilize one or more LCDs to alter the orientation of the electric field vector (see FIG. 7) of the light being projected. The birefringence of the individual LCD pixels are selectively altered by suitable apparatus such as cathode ray tubes, lasers, or electronic circuit means. A typical liquid crystal light valve (LCLV) projector includes a source lamp which is used to generate a light beam that is directed through a polarizer. This polarized light is directed through the LCDs to change the polarization according to the image to be displayed. The light, after exiting the LCD, passes through a plastic polarizer analyzer which stops and absorbs the unwanted portion of light. The formed image is then enlarged with a projection lens system for forming an enlarged picture on a display screen.
Color LCLV projectors typically include color separating apparatus such as a prism, beam splitters or dichroic mirrors to separate collimated white light beams from the light source into three primary color beams (i.e., red, green and blue beams). The red, green and blue beams are then individually modulated by LCDs and combined by separate optical apparatus such as combining prisms, mirrors or lenses.
In general, the quality and brightness of the projected image in any LCLV projector is a function of the brightness of the source for illuminating the LCDs and the polarizing means. Polarizing optics must be utilized to filter/separate the white light into light with a single orientation of the electric field vector. The white light emitted from the source is thus only partially utilized (i.e., one direction of polarization) in most LCLV projection systems. This requires oversized light sources to achieve a desired brightness at the viewing screen.
Typically, with a twisted nematic transmissive type LCD cell surrounded by plastic polarizers, only forty percent or less of the output of the light source is utilized. Practically, only a maximum transmission of 50% for randomly polarized light passed through could ever be achieved because of the construction and principles involved in plastic polarizers, allowing for 100% efficiency for the device for all wavelengths. Thus, it is impossible to obtain a full brightness projector. Moreover, the unused polarized component of the light source is absorbed by the plastic polarizers and generates wasted energy in the form of heat and transfers this heat to other components (i.e., LCDs, electronics, etc.) and hence is detrimental to the system (especially the plastic polarizers, LCDs, electronics, etc.). This heat must be either shielded and/or dissipated from the components of the system, or else, the light source must be reduced in light output so that the amount of light being absorbed is below the threshold of permanent damage to the components, including the plastic polarizers. Currently, this threshold for fabricated plastic polarizers is between the range of 5-10 watts of light per square inch (0.78-1.55 watts per square centimeter), depending upon the wavelength of the illuminating light. A method for improving the damage threshold is included in U.S. Pat. No., 5,071,234 to Amano, et aL, although this patent does not discuss the particulars of what the damage threshold is.
Prior art systems have required relatively complicated optical systems including the use of polarizing prisms and prepolarizing prisms to ensure a unitary or single polarization at the LCD and to provide a suitable resolution and contrast of the projected image. With prior art color LCLV projectors, complicated optic components and arrangements are required to combine the separated color bands at a suitable resolution and contrast.
Representative prior art LCLV projectors are disclosed in U.S. Pat. No. 5,060,058 to Goldenberg, et al, U.S. Pat. No. 5,048,949 to Sato, et al., U.S. Pat. No. 4,995,702 to Aruga, et al., U.S. Pat. No. 4,943,154 to, Miyatake, et al., U.S. Pat. No. 4,936,658 to Tanaka, et al., U.S. Pat. No. 4,936,656 to Yamashita, et al., U.S. Pat. No. 4,935,758 to Miyatake, et al., U.S. Pat. No. 4,911,547 to Ledebuhr, U.S. Pat. No. 4,909,601 to Yajima, et al., U.S. Pat. No. 4,904,061 to Aruga, et al., U.S. Pat. No. 4,864,390 to McKechnie, U.S. Pat. No. 4,861,142 to Tanaka, et al., U.S. Pat. No. 4,850,685 to Kamakura, U.S. Pat. No. 4,842,374 to Ledebuhr, U.S. Pat. No. 4,836,649 to Ledebuhr, et al., U.S. Pat. No. 4,826,311 to Ledebuhr, U.S. Pat. No. 4,786,146 to Ledebuhr, U.S. Pat. No. 4,772,098 to Ogawa, U.S. Pat. No. 4,749,259 to Ledebuhr, U.S. Pat. No. 4,739,396 to Hyatt, U.S. Pat. No. 4,690,526 to Ledebuhr, U.S. Pat. No. 4,687,301 to Ledebuhr, U.S. Pat. No. 4,650,286 to Koda, et al., U.S. Pat. No. 4,647,966 to Phillips, et al., U.S. Pat. No. 4,544,237 to Gagnon, U.S. Pat. No. 4,500,172 to Gagnon, U.S. Pat. No. 4,464,019 to Gagnon, U.S. Pat. No. 4,464,018 to Gagnon, U.S. Pat. No. 4,461,542 to Gagnon, U.S. Pat. No. 4,425,028 to Gagnon, U.S. Pat. No. 4,191,456 to Hong, et al., U.S. Pat. No. 4,127,322 to Jacobson, et al., U.S. Pat. No. 4,588,324, to Marie, U.S. Pat. No. 4,943,155 to Cross, Jr., U.S. Pat. No. 4,936,657 to Tejima, et al., U.S. Pat. No. 4,928,123 to Takafuji, U.S. Pat. No. 4,922,336 to Morton, U.S. Pat. No. 4,875,064 to Umeda, U.S. Pat. No. 4,872,750 to Morishita, U.S. Pat. No. 4,824,210 to Shimazaki, U.S. Pat. No. 4,770,525 to Umeda, et al., U.S. Pat. No. 4,715,684 to Gagnon, U.S. Pat. No. 4,699,498 to Naemura, et al., U.S. Pat. No. 4,693,557 to Fergason, U.S. Pat. No. 4,671,634 to Kizaki, et al., U.S. Pat. No. 4,613,207 to Fergason, U.S. Pat. No. 4,611,889 to Buzak, U.S. Pat. No. 4,295,159 to Carollo, et al.
Prior art illumination systems for overcoming problems with the brightness of LCD display illumination systems have not been completely successful.
An example of an illumination system that attempts to utilize the full output of a light source for increasing the brightness of an LCD display is disclosed in U.S. Pat. No. 5,028,121 to Baur, et al. In the Baur system, the randomly polarized light source is resolved into two separate polarized beams, with one of the polarized beams passed to a dichroic color splitter that then directs the segregated color beams to a set of reflecting LCDs, while the other beam of different polarization is sent to a different set of LCDs through a different dichroic splitter. After having each respective portion of the beams' electric field vector altered, the beam is then reflected back through the dichroic mirrors into the polarizing beam splitter/combiner. The picture to be represented is sent to the projection lens, while the rejected beam is sent back into the light source. This causes the light source to heat and have a shortened life span. Furthermore, each sequential field to be projected has a different brightness level illuminating each pixel, depending upon the amount of light that is rejected back into the light source.
For example, if a light source has an average output of 1000 lumens and the sequential field to be projected has an average brightness level of 30%, then 700 lumens would be reflected back into the light source, making the light emitted from the source to be an effective 1700 lumens. In the next sequential field, if the average brightness level is 50%, then 500 lumens would be reflected back into the light source, making the light emitted from the source to be an effective 1500 lumens. This can be alleviated by computing the average brightness level to be projected, and then modulating the brightness level of the light source when the field is changed for projection so that the the illumination of a pixel is at a constant brightness. This system can further be modified by (or be a stand alone system) that would monitor the light output of the light source and change the driving circuitry of the light source to maintain a constant brightness level. This can be monitored by a light transducer that monitors the light from a beam splitter, or alternately, can be mounted directly on a LCD panel outside of the picture forming active area. However, the addition of any of the above circuitry further complicates the projector and makes the light source an active part of the system, increasing the cost and complexity of the projector.
Another example of an illumination system that attempts to utilize the full output of a light source for increasing the brightness of an LCD display is disclosed in U.S. Pat. No. 4,913,529 to Goldenberg, et al. In the Goldenberg system, a beam of light, from a light source, is split into two orthogonally linear polarized beams. One of the beams is then passed through a device that rotates one of the beams to change its direction of polarization so that there are two beams of the same polarization. The beams of the same polarization are then directed through different faces of a prism, combined by the prism and focused on the LCD devices.
A problem with such a system is that the beams are not collinear. The beams illuminate the polarizer at different angles, causing an area of usable light, and another area of unusable light. The result is that all of the light available is not used. Another obstacle is that it is difficult to align the combined beams with the use of a prism. Yet another complication is that the prism tends to separate the light into separate colors. This detracts from the clarity, brightness and limits the resolution of the projected image. Still another complication is that the performance of polarizers vary with the angle of light illuminating them, causing different polarizations and different color gradations to occur in the beam.
Other systems, such as those disclosed in U.S. Pat. No. 4,824,214 to Ledebuhr, U.S. Pat. No. 4,127,322 to Jacobson, et al., U.S. Pat. No. 4,836,649 to Ledebuhr, et al., and U.S. Pat. No. 3,512,868 to Gorklewiez, et al. also disclose optical layouts for achieving a high brightness in display systems that utilize LCD devices. In general, these systems are relatively complicated and contain numerous components that are large, expensive, and difficult to adjust.
Representative prior art flat fluorescent light sources are disclosed in U.S. Pat. No. 4,978,888 to Anandan, et al. and U.S. Pat. No. 4,920,298 to Hinotani, et al.
Representative prior art light integrators for light sources are disclosed in U.S. Pat. No. 4,918,583 to Kudo, et al., U.S. Pat. No. 4,787,013 to Sugino, et al. and U.S. Pat. No. 4,769,750 to Matsumoto, et al. Various prior art techniques and apparatus have been heretofore proposed to present 3-D or stereographic images on a viewing screen, such as on a polarization conserving motion picture screen. See U.S. Pat. No. 4,955,718 to Jachimowicz, et al., U.S. Pat. No. 4,963,959 to Drewio, U.S. Pat. No. 4,962,422 to Ohtomo, et al., U.S. Pat. No. 4,959,641 to Bess, et al., U.S. Pat. No. 4,957,351 to Shioji, U.S. Pat. No. 4,954,890 to Park, U.S. Pat. No. 4,945,408 to Medina, U.S. Pat. No. 4,936,658 to Tanaka, et al., U.S. Pat. No. 4,933,755 to Dahl, U.S. Pat. No. 4,922,336 to Morton, U.S. Pat. No. 4,907,860 to Noble, U.S. Pat. No. 4,877,307 to Kalmanash, U.S. Pat. No. 4,872,750 to Morishita, U.S. Pat. No. 4,870,486 to Nakagawa, U.S. Pat. No. 4,853,764 to Sutter, U.S. Pat. No. 4,851,901 to Iwasaki, U.S. Pat. No. 4,834,473 to Keyes, et al., U.S. Pat. No. 4,807,024 to McLaurin, et al., U.S. Pat. No. 4,799,763 to Davis, U.S. Pat. No. 4,772,943 to Nakagawa, U.S. Pat. No. 4,736,246 to Nishikawa, U.S. Pat. No. 4,649,425 to Pund, U.S. Pat. No. 4,641,178 to Street, U.S. Pat. No. 4,541,007 to Nagata, U.S. Pat. No. 4,523,226 to Lipton, et al., U.S. Pat. No. 4,376,950 to Brown, et al., U.S. Pat. No. 4,323,920 to Collendar, U.S. Pat. No. 4,295,153 to Gibson, U.S. Pat. No. 4,151,549 to Bautzc, U.S. Pat. No. 3,697,675 to Beard, et al. In general, these techniques and apparatus involve the display of polarized or color sequential two-dimensional images which contain corresponding right eye and left eye perspective views of three-dimensional objects. These separate images can also be displayed simultaneously in different polarizations or colors. Suitable eyeware, such as glasses having different polarizing or color separating coatings, permit the separate images to be seen by one or the other eye. This type of system is relatively expensive and complicated requiring two separate projectors and is adapted mainly for stereoscopic movies for theaters. U.S. Pat. No. 4,954,890 to Park discloses a representative projector employing the technique of alternating polarization.
Another technique involves a timed sequence in which images corresponding to right-eye and left-eye perspectives are presented in timed sequence with the use of electronic light valves. U.S. Pat. No. 4,970,486 to Nakagawa, et al., and U.S. Pat. No. 4,877,307 to Kalmanash disclose representative prior art stereographic display systems of this type.
While previous time sequential light valve systems are adaptable to display arrangements for a television set, because of problems associated with color, resolution and contrast of the projected image, they have not received widespread commercial acceptance. Moreover, the systems proposed to date have also been relatively expensive and complicated.